Novel formulation of phosphorus fertilizer for plants

ABSTRACT

Concentrated phosphorus fertilizers are disclosed that comprise a buffered composition of an organic acid and salts thereof and a phosphorous-containing acid and salts thereof. The concentrated phosphorus fertilizers can be diluted with water of pH ranging from about 6.5 to about 8.5 at ratios of concentrate to water at about 1:40 to about 1:600 to result in a fertilizer having a pH in the range acceptable for foliar uptake of phosphorus.

BACKGROUND OF THE INVENTION

[0001] Fertilizers are added to the soil of crops or in some cases theycan be applied directly to crop foliage to supply elements needed forplant nutrition. Seventeen elements are known to be essential to thehealth and growth of plants. Typically, nitrogen, phosphorus, andpotassium are provided in the greatest quantity. With increasingknowledge of the role of each of the nutrients essential to plants,there is a better understanding of the importance of providing a givennutrient at the appropriate stage of phenology. To accomplish this,rapid changes in fertilizer formulations and methods of application havebeen necessary.

[0002] Another factor changing fertilization formulations and methods isdue to pressure from federal, state and local regulatory agencies andcitizen groups to reduce the total amount of fertilizer in general, andof specific nutrients in particular, being applied to the soil.Additionally, the loss of registration of existing synthetic plantgrowth regulators and organic pesticides and the prohibitively highcosts involved in the successful registration of new ones, also plays arole in the changing arena of crop fertilization.

[0003] The principal source of phosphorus for the fertilizer industry isderived from the ores of phosphorus-containing minerals found in theEarth's crust, termed phosphate rock. Elemental phosphorus does notexist in nature; plants utilize phosphorus as the dihydrogen phosphateion (H₂PO₄ ⁻). While untreated phosphate rock has been used forfertilizer, it is most commonly acidulated with dilute solutions ofstrong mineral acids to form phosphoric acid, which is more readilyabsorbed by crops.

[0004] Until recently, phosphate and polyphosphate compounds wereconsidered the only forms in which phosphorus could be supplied toplants to meet the plant's nutritional need for phosphorus. Indeed, theonly phosphite compound cited for use as a fertilizer in the Merck Index(M. Windhols, ed., 1983, 10th edition, p.1678) is calcium phosphite(CaHPO₃). No phosphite fertilizer formulations are listed in The FarmChemical Handbook (Meister Publishing Co., 1993, Willoughby, Ohio 834p.) or Western Fertilizer Handbook (The Interstate, Danville, Ill. 288p.) Historically, calcium phosphite was formed as a putative contaminantin the synthesis of calcium superphosphate fertilizers [McIntyre et al.,Agron. J. 42:543-549 (1950)] and in one case, was demonstrated to causeinjury to corn [Lucas et al., Aaron. J. 71:1063-1065 (1979)].Consequently, phosphite was relegated for use only as a fungicide(Alliete®; U.S. Pat. No. 4,075,324) and as a food preservative.

[0005] More recently, it has been shown that plants can obtainphosphorus from phosphite [Lovatt, C. J., Mar. 22, 1990, “Foliarphosphorus fertilization of citrus by foliar application of phosphite”In: Citrus Research Advisory Committee (eds) Summary of Citrus Research,University of Calif., Riverside, Calif. pp 25-26; Anon., May, 1990,“Foliar applications do double duty” In: L. Robison (ed) Citrograph Vol.75, No. 7, p 161; Lovatt, C. J., 1990, “A definitive test to determinewhether phosphite fertilization can replace phosphate fertilization tosupply P in the metabolism of ‘Hass’ on ‘Duke 7’:—A preliminary report”California Avocado Society Yearbook 74:61-64; Lovatt, C. J., 1992].Formulations based on phosphorous acid and hypophosphorous acid, asphosphite is, generally undergo oxidation to phosphate and thus lose thebenefits that could be derived from the use of phosphite fertilizationapplications.

[0006] The phosphate and polyphosphate fertilizers currently used have anumber of properties that compromise their desirability as fertilizers.Generally, they tend to form precipitates during storage and shipping.This limits the ability to formulate concentrated solutions offertilizers. Additionally, formulations must generally be maintained ata narrow pH range to prevent precipitation, resulting in fertilizersthat are limited to particular uses.

[0007] Another drawback of phosphate fertilizers is that they are notreadily taken up by the foliage of many plants and must instead bedelivered to the soil for uptake by plant roots. The mobility ofphosphate fertilizers in the soil is limited leading to rapid localizeddepletion of phosphorus in the rhizosphere and phosphorus deficiency ofthe plant. Frequent reapplication of phosphate fertilizers isundesirable because it leads to leaching of phosphate into thegroundwater resulting in eutrophication of lakes, ponds and streams.

[0008] Phosphate and polyphosphate fertilizers have also been shown toinhibit the beneficial symbiosis between the roots of the plants andmycorrhizal fungi. They tend to support the growth of algae and promotebacterial and fungal growth in the rhizosphere, including the growth ofpathogenic fungi and other soil-borne pests.

[0009] Even though phosphorus, once in the plant, is very phloem mobile(i.e. readily moving from old leaves to young tissues), phosphate ispoorly absorbed through the leaves of most plant species. This isunfortunate because successful foliar phosphorus feeding would result inthe application of less phosphate fertilizers to the soil and reducephosphorus pollution of the ground water.

[0010] Accordingly, there is a need for a phosphorus fertilizer that canbe utilized in irrigation systems and applied to foliage without theformation of precipitates that reduce nutrient availability and uptakeby the plant and plug emitters and sprayers. There is also a need fornew methods of fertilizer application that allow nutrients in a readilyavailable form to be supplied at the exact time the plant needs them.This need includes the facility of a foliar product to be sold in asingle formulation for use as a concentrated material for airplane orhelicopter application or as a dilute solution for ground sprayapplication and yet able to be maintained at a suitable pH range optimalfor leaf uptake despite the need to be diluted prior to application.

[0011] Additionally, there is a demand for phosphorus fertilizers thathave the facility to be used as liquids or solids (granule or powder).There is also a demand for fertilizers that do more than just supplynutrients. It is desired that the fertilizers also have demonstratedplant growth regulator activity, increase the plants' resistance topests, promote plant health in general and root health in particular,increase the production of allelopathic compounds, increase pre- andpost-harvest quality, improve stress tolerance, enhance beneficialsymbioses, and improve yield over existing traditional soil or foliarfertilizers.

SUMMARY OF THE INVENTION

[0012] Given the above-mentioned deficiencies and demands of fertilizersin general, and of phosphorus fertilizers in particular, it is an objectof the present invention to provide phosphorus to plants in aformulation that renders phosphorus readily available to the plantsunder a number of application methods such as through soil, foliaruptake, irrigation, and other methods.

[0013] It is also an object that the phosphorus fertilizer formulationsbe conveniently formulated in concentrated solutions that are stableduring storage and shipping.

[0014] Another object of the present invention is to provide aphosphorus fertilizer that is not as inhibitory to mycorrhizal fungi astraditional phosphate fertilizers.

[0015] It is a further object of the present invention to provide aphosphorus fertilizer that does not support the growth of algae to thesame degree that traditional phosphate fertilizers do.

[0016] Additional objects and features of the invention will be apparentto those skilled in the art from the following detailed description andappended claims.

[0017] The above objects and features are accomplished by a concentratedphosphorus fertilizer comprising a buffered composition comprising anorganic acid and salts thereof and a phosphorous-containing acid andsalts thereof. The concentrated phosphorus fertilizer can be dilutedwith water of pH ranging from about 6.5 to about 8.5 at ratios ofconcentrate to water at about 1:40 to about 1:600 to result in a fullysolubilized fertilizer having a pH in a range acceptable for foliaruptake of phosphorus.

[0018] In one embodiment, the phosphorous-containing acid is selectedfrom the group consisting of phosphorous acid, hypophosphorous acid,polyphosphorous acid, and polyhypophosphorous acid and the organic acidis preferably selected from the group consisting of dicarboxylic acidsand tricarboxylic acids such as citrate.

[0019] In one embodiment, the concentrated phosphorus fertilizer is anessentially clear liquid devoid of precipitate that can be diluted at aratio of about 1:40 to about 1:600 with water having pH of about 6.5 toabout 8.5, to result in a fertilizer having a pH of about 5.0 to about7.0, and more preferably from about 5.5 to about 6.5, to facilitate theuptake of phosphorus by a variety of plants.

[0020] A method of providing phosphorus to plants is also disclosed. Themethod comprises diluting a concentrated phosphorus fertilizercomprising a buffered composition comprising an organic acid and saltsthereof and a phosphorous-containing acid and salts thereof with waterto form a substantially fully solubilized use-dilution fertilizer havinga pH in a range acceptable for foliar uptake of phosphorus, and applyingthe fertilizer to the plant foliage.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention provides phosphorus fertilizers essentiallydevoid of phosphate. The fertilizer comprises a double or multiplebuffer system of organic acids and their salts with aphosphorous-containing acids and their salts. The formulation stabilizesthe phosphorous against oxidation to phosphate. Suitablephosphorous-containing acids are phosphorous acid and polyphosphorousacid, based generally on the formula H₃PO₃, and hypophosphorous acid andpolyhypophosphorous acid, based generally on the formula H₃PO₂.Phosphite, the salt of phosphorous acid, has properties that are knownto be beneficial to crop production. It is taken up through the foliageof avocado and citrus, two species which classically do not take upphosphate through their foliage. Phosphite has fungicidal propertieswith regard to some species of pathogenic fungi: Rhizoctonia solani,Botrytis cinerea, Piricularia oryzae, Plasmopora viticola, Phytophthoracinnamomi, and Phytophthora parasitica. Recently, it has beendemonstrated that phosphite also serves as a source of metabolicallyactive phosphorus in plants. The properties of phosphite that make itdesirable as a fertilizer are enhanced when it is formulated accordingto the present invention as a double or multiple buffer with phosphorousacid, hypophosphorous acid, polyphosphorous acid and/orpolyhypophosphorous acid and their respective salts and organic acidsand their salts per this invention.

[0022] Suitable organic acids have the formula R—COOH or R—COO⁻ where Ris hydrogen or a carbon-containing molecule or group of molecules.Suitable organic acids are those that maintain the phosphite ion in asubstantially fully solubilized form upon dilution with water at pHvarying from about 6.5 to about 8.5 and that result in a use-dilutionfertilizer having a foliage-acceptable pH for phosphorus uptake.Preferred organic acids are dicarboxylic and tricarboxylic acids.

[0023] By the term “substantially fully solubilized” it is meant thatupon dilution, the phosphite does not precipitate, or at least notappreciably, so as to affect administration of the liquid product to theplant foliage, and thus is in a form available to the plant. Withpresent phosphite fertilizers, there is a tendency for phosphite toprecipitate if diluted with alkaline water, thereby rendering thephosphite in a form that is unavailable to the plant for uptake.

[0024] By the term “foliage-acceptable pH for phosphorus uptake”, it ismeant a pH that allows phosphorus to be absorbed by the plant withoutcausing damage to the foliage. A foliage-acceptable pH for phosphorusuptake usually ranges between about 5.0 to about 7.0, and preferablybetween about 5.5 to about 6.5. Phosphorus is most readily taken up byfoliage at pH 6.0. Depending on the plant species, a pH below 5.0 cancause damage to leaves and/or the flowers and/or fruit. At higher pH,between about 7.0 to about 7.5, there is reduced uptake of nutrients,although generally there is no plant damage. A pH between about 7.5 and8.0, depending on the plant species, plant damage may result. A pHgreater than 8.0, generally causes damage to the plant in addition toreducing uptake of the nutrients. Accordingly, suitable organic acidsare those that help provide a “buffered composition” having the desiredpH range. This means that a “use-dilution fertilizer” having an acidicto neutral pH (pH 5.0 to 7.0) can be achieved upon high dilutions (up toabout {fraction (1/600)}) of the concentrated fertilizer with highlyalkaline water (up to a pH of about 8.5).

[0025] Organic acids that meet this criteria include but not limited tointermediates in the Kreb's Tricarboxylic Acid Cycle, amino acids suchas glutamic acid and aspartic acid, vitamin acids such as ascorbic acidand folic acid, and their respective salts. Particularly preferredorganic acids are dicarboxylic and tricarboxylic acids selected from thegroup consisting of citrate, pyruvate, succinate, fumarate, malate,formate, oxaloacetate, citrate, cis-aconitate, isocitrate, andα-ketoglutarate. Citrate is a particularly preferred organic acidbecause of it is relatively inexpensive and readily available.

[0026] These formulations allow the maintenance of continued solubility,and thus availability for uptake by plants, of phosphorus, with orwithout other nutrients, over a significantly wide range ofconcentrations and pHs. The increased solubility of these formulationover that of phosphate or phosphite fertilizers makes it possible toprepare fertilizers with a greater concentration of phosphorus per unitvolume than traditional phosphate or polyphosphate fertilizers or thesimple unbuffered salts of phosphorous acid recently being marketed asfertilizers for foliar application which are available as supersaturated solutions with only about 16% phosphite, and which are dilutedapproximately 1:100 to about 1:300. The resulting pH of thesefertilizers varies significantly depending upon the pH of the waterused, thus affecting the availability of the nutrients for foliaruptake. In contrast, the highly concentrated fertilizers of the presentinvention, which can be diluted with water at a ratio of about 1:600,allow for more cost effective shipping, handling, and application. Theyresult in greater uptake of phosphorus by the canopy of plants thantraditional phosphate or recent phosphite fertilizers not formulated inthis manner.

[0027] The formulations provided herein also make it possible toformulate various combinations of other essential plant nutrients orother inorganic or organic compounds as desired and maintain theirsolubility when used over a wide range of concentrations and pHs, whichis not possible for present phosphate or phosphite fertilizers. Forexample, boron, manganese, calcium; iron and other elements can beprovided at relatively high concentrations in these formulations. Thus,these phosphorus fertilizers also enhance the canopy uptake of othermineral nutrients essential to plants. They can be used as a canopyapplication to improve pre- and post-harvest crop quality.

[0028] Formulations can also prepared with copper. However, when highconcentrations of copper are used, the copper is not-fully solubilized.In this situation, the insoluble copper is desirable as it preventsrapid uptake of the copper and thus minimizes the potential for coppertoxicity. As the insoluble copper is rewetted over night by dew,dissolution occurs so that additional copper is taken up. The bufferingcapacity of the formulation maintains the pH at a foliage-acceptable pHwhen the insoluble copper is rewetted so that conditions are optimal foruptake and are benign to the plant tissues. While copper is an elementessential to plants, it is required in only small amounts. In relationto nitrogen, plants require, in general, 10,000- to 75,000-fold lesscopper. Provided to the foliage of the plant at the rate provided bythis formulation, copper is a very effective fungicide, in addition tobeing a plant nutrient and fertilizer.

[0029] In addition to the above-mentioned advantages, the formulationsdisclosed have a direct benefit to the environment. Because theformulations allow successful foliar feeding of phosphorus to a numberof plants that do not effectively take up phosphorus when supplied inphosphate or polyphosphate forms, and because these formulations enhancethe uptake of other nutrients, they are cost-effective and can replaceless efficient, traditional soil-feeding methods. This results inreducing phosphate pollution of the groundwater and eutrophication offreshwater ponds, lakes and streams.

[0030] The phosphorus fertilizers disclosed herein can also beadvantageously applied through the soil or by irrigation systems assolid (granular) or liquid formulations. These formulations can be usedat pHs sufficiently low to clean irrigation lines and alter the pH ofthe soil to solve alkalinity problems while supplying essentialnutrients to plants. Example 2, below discloses a suitable formulationfor irrigation application. With irrigation application, the fertilizerflowing through the irrigation system will typically have a pH lowerthan about 2.5, usually less than about pH 1.5. The low pH is designedto supply phosphorus while killing bacteria and algae (slime) which plugirrigation lines, thus cleaning the lines. The low pH also dissolvescalcium carbonate deposits at and around the emitters, and solubilizesthe calcium carbonate so Ca²⁺ is available to the plant. Once deliveredto the soil near the plant, sufficient water is applied to achieve a pHsuitable for phosphorus uptake by the plant. The form in which thephosphorus is supplied in these formulations is more mobile thanphosphate fertilizers or than the simple salts of phosphorous acidrecently being sold as fertilizers, and thus more available and morereadily taken up by the roots of plants. An advantage of theseformulations is that the form in which phosphorus is supplied does notinhibit the development of mycorrhizal fungi to the same degree thattraditional phosphate fertilizers do. The present compositions can alsobe formulated with certain nutrients in addition to phosphorus that arereadily absorbed through soil applications at pH of about 5.5 to about7.0. Such nutrients include nitrogen, calcium, magnesium, potassium,molybdenum, boron, and sulfur.

[0031] Another advantage with the phosphorus fertilizers disclosedherein is that they do not support the growth of green algae to the samedegree that traditional phosphate fertilizers do. This is of significantimportance to agriculture, commercial nurseries, the ornamental and cutflower industry, and the home and garden industry, as it will preventthe growth of green algae which typically proliferate and plugirrigation emitters, foul pots and benches, and provide a niche for thegrowth of pathogenic bacteria and fungi. These formulations also endowthe phosphorus fertilizer with anti-viral, anti-bacterial andanti-fungal activity. This bacterialcidal activity in a phosphorusfertilizer makes it possible to use this fertilizer to inhibitice-nucleating bacteria to thus protect plants from frost damage.

[0032] Methods of Preparation

[0033] The phosphorus fertilizers are prepared by first formingsolutions of the phosphorous and organic acids. Other desired nutrientscan then be added with constant stirring. The amount of phosphorousrelative to organic acid is not critical, as long as appropriatebuffering and solubility are achieved. Generally the amount of organicacid that is added will depend upon the form in which the nutrientelements are added. For example, if calcium is to be added in the formof calcium hydroxide (a base), then the acid form of the organic acid,for example citric acid, would be used rather than its salt, citrate. Inaddition to the desired nutrients, other additives, that are known inthe fertilizer industry, can be added. These include, for example,wetting-agents, surfactants, spreaders, stickers etc., and are describedin The Farm Chemical Handbook, supra (incorporated herein by reference).The fertilizer compositions can also be prepared as solid formulations,identical to the liquid ones by simply leaving out all of the water. Theproperties are the same as the liquid formulations but have theadditional advantage of weighing less for the same amount of nutrient.

[0034] Methods of Application

[0035] The fertilizer is applied according to crop-specificrecommendations which will depend upon the application method (foliar,soil, irrigation, etc.), time of application, rate of application, andproduct formulation. Crops that will benefit from the fertilizerinclude, but are not limited to, avocado, citrus, mango, coffee,deciduous tree crops, grapes and other berry crops, soybean and othercommercial beans, corn, tomato, cucurbits and cucumis species, lettuce,potato, sugar beets, peppers, sugarcane, hops, tobacco, pineapple,coconut palm and other commercial and ornamental palms, hevea rubber,and ornamental plants.

[0036] In addition to the foliar, soil, and irrigation applicationmethods mentioned above, the present fertilizer may prove beneficial tocertain crops through other application methods. For example, trunkpaints or other methodologies may provide for a continuous low supply offertilizers, such as, for example, “intravenous” feeding as practiced inthe boron nutrition of soybeans.

[0037] In order that the invention described herein may be more fullyunderstood, the following examples are set forth. All chemicals usedwere of analytical reagent quality and approximately 100% by weightunless otherwise specified. All formulations are expressed in terms ofweight to volume. It should be understood that these examples are forillustrative purposes only and are not to be construed as limiting thescope of the invention in any manner.

EXAMPLE 1

[0038] A formulation was prepared of 1 gallon of 0-40-0 fertilizer with3.86 lbs H₃PO₃, I.34 lbs tripotassium citrate, 1.34 lbs of trisodiumcitrate, and 4.0 lbs of 58% ammonium hydroxide. The components weredissolved in water with constant stirring. This single formulation canbe used at a rate of 2 quarts in as little as 20 gallons of water of pH6.5 to 8.5 up to 300 gallons of water of pH 6.5 to 8.5 and maintain a pHbetween 5.5 to 6.5 without the formation of any precipitate.

EXAMPLE 2

[0039] A formulation was prepared of 1 gallon of 0-40-0 fertilizer with3.86 lbs H₃PO₃ and 0.5 lbs citric acid. This formulation is stable at pH1.0 or less and is designed for application through the irrigationsystem. It is stable against oxidation and precipitation when suppliedthrough the irrigation water.

EXAMPLE 3

[0040] A formulation was prepared of 1 gallon of 0-30-0 fertilizer with74.89% elemental boron with 2.89 lbs H₃PO₃, 28.67 lbs borax (Na₂B₄O₇10H₂O), 17.16 lbs boric acid (H₃BO₃), 1.54 lbs H₂SO₄ and 2.67 lbs citricacid. A solution of the phosphorous and citric acid was first prepared,then the other elements were added with constant stirring. Thisformulation can be used at the rate of 2 quarts in as little as 20gallons of water of pH between 6.5 to 8.5 up to 300 gallons of water ofpH 6.5 to 8.5 and maintain a pH between 5.5 to 6.5 without the formationof any precipitate.

EXAMPLE 4

[0041] A formulation was prepared of 1 gallon of 0-30-0 fertilizer with21.57% Zn and 23.22% Mn with 2.89 lbs of H₃PO₃, 7.92 lbs ZnSO₄, 7.16 lbsMn(H₂PO₂)₂H₂0, 0.61 lbs citric acid and 0.87 lbs 58% NH₄OH. Thisformulation can be used at the rate of two quarts in as little as 20gallons of water of pH between 6.5 to 8.5 up to 300 gallons of water ofpH between 6.5 to 8.5 and maintain a pH between 5.5 to 6.5 without theformation of any precipitate.

EXAMPLE 5

[0042] A formulation was prepared of 1 gallon of 0-30-0 fertilizer with5.4% Ca. It was packaged in a two-container system where 1 gallon ofsolution A contained 2.89 lbs H₃PO₃, 0.68 lbs Ca(OH)₂, and 0.28 lbscitric acid, and 1 gallon of solution B contained 0.16 lbs Ca(OH)₂, 0.60lbs KOH, 3.34 lbs 58% NH₄OH, 0.28 lbs citric acid, and 0.67 lbs EDTA(ethylenediaminetetraacetic acid). Two quarts of solution A can be addedto as little as 20 gallons of water of pH between 6.5 to 8.5 up to 300gallons of water of pH between 6.5 to 8.5 followed by the addition oftwo quarts of solution B. The final solution is between pH 5.5 to 6.5and without precipitation.

[0043] A formulation of 1 gallon of 0-30-0 fertilizer with 4.32% Ca canbe made without requiring EDTA. This formulation is also packaged in atwo-container system where 1 gallon of solution A contains 2.89 lbsH₃PO₃, 0.67 lbs Ca(OH)₂ and 0.28 lbs of citric acid, while 1 gallon ofsolution B contains 2.67 lbs of 58% NH₄OH, 0.6 lbs KOH. Two quarts ofsolution A can be added to as little as 20 gallons of water of pHbetween 6.5 to 8.5 up to 300 gallons of water of pH between 6.5 and 8.5followed by the addition of two quarts of solution B. The final pH ofthe solution is between 5.5 and 6.5 and without precipitation.

EXAMPLE 6

[0044] A formulation was prepared of 1 gallon of 0-30-30 fertilizer with2.89 lbs H₃PO₃, 2.99 lbs KOH, and 0.84 lbs citric acid. Two quarts canbe added to as little as 20 gallons of water of pH between 6.5 to 8.5and up to 300 gallons of water of pH between 6.5 and 8.5. The pH of thefinal solution is between 5.5 and 6.5 without precipitation.

EXAMPLE 7

[0045] A formulation was prepared of 1 gallon of 0-30-0 fertilizerhaving 4.8% iron with 2.89 H₃PO₃, 1.75 lbs iron-citrate, 0.74 lbs KOH,0.62 lbs NaOH, and 2.00 lbs of 58% NH₄OH. Two quarts of the formulationcan be added to as little as 20 gallons of water pH 6.5 to 8.5 and up to300 gallons of water of pH 6.5 to 8.5. The pH of the final solution isbetween 5.5 to 6.7 without precipitation.

EXAMPLE 8

[0046] A formulation was prepared of 1 gallon of 0-30-0 fertilizerhaving 23.22% manganese with 2.89 H₃PO₃, 7.16 lbs. Mn(H₂PO₂)₂, and 0.133lbs. sodium citrate. Two quarts of the formulation can be added to aslittle as 20 gallons of water pH 6.5 to 8.5 and up to 300 gallons ofwater of pH 6.5 to 8.5. The pH of the final solution is between 5.5 to6.5 without precipitation.

EXAMPLE 9

[0047] A formulation was prepared of 1 gallon of 0-30-0 fertilizerhaving 57% copper with 2.89 H₃PO₃, 7.3 lbs Cu(OH)₂ (57% Cu), and 1.34lbs of 58% NH₄OH. Two quarts can be added to as little as 20 gallons ofwater of pH 6.5 to 8.5 up to 300 gallons of water of pH 6.5 to 8.5. ThepH of the final solution is between 5.5 to 6.5. The copper is not fullysoluble, however this is desirable in that it prevents the rapid uptakeof copper when applied to plant foliage.

What is claimed is:
 1. A concentrated phosphorus fertilizer comprising abuffered composition comprising an organic acid and salts thereof and aphosphorous-containing acid and salts thereof, such that when saidcomposition is diluted with water, there is formed a substantially fullysolubilized use-dilution fertilizer having a foliage-acceptable pH forphosphorus uptake.
 2. The phosphorus fertilizer of claim 1 wherein saidphosphorous-containing acid is selected from the group consisting ofphosphorous acid, hypophosphorous acid, polyphosphorous acid, andpolyhypophosphorous acid.
 3. The phosphorus fertilizer of claim 1wherein said organic acid is selected from the group consisting ofdicarboxylic acids and tricarboxylic acids.
 4. The phosphorus fertilizerof claim 3 wherein said organic acid is citrate.
 5. The phosphorusfertilizer of claim 1 wherein said use-dilution fertilizer has a pH ofabout 5.0 to about 7.0.
 6. The phosphorus fertilizer of claim 1 whereinsaid use-dilution fertilizer has a pH of about 5.5 to about 6.5.
 7. Thephosphorus fertilizer of claim 1 wherein said water has a pH of about6.5 to about 8.5.
 8. The phosphorus fertilizer of claim 1 that isessentially clear and devoid of precipitate.
 9. The phosphorusfertilizer of claim 1 wherein said use-dilution fertilizer comprises aratio of said concentrated phosphorus fertilizer to said water of about1:40 to about 1:600.
 10. The phosphorus fertilizer of claim 1 whereinsaid phosphorus-containing acid is present in an amount of about 30 toabout 40 weight percent.
 11. A concentrated phosphorus fertilizercomprising a buffered composition comprising an organic acid and saltsthereof, a phosphorous-containing acid and salts thereof, and copper,such that when said composition is diluted with water, there is formed ause-dilution fertilizer having a foliage-acceptable pH for phosphorusuptake.
 12. A concentrated phosphorus fertilizer for irrigationapplication, said fertilizer comprising a buffered compositioncomprising an organic acid and salts thereof and aphosphorous-containing acid and salts thereof, said composition having apH less than about 2.5.
 13. The phosphorus fertilizer of claim 12 havinga pH of less than about 1.5.
 14. A method of providing phosphorus to aplant comprising diluting a concentrated phosphorus fertilizercomprising a buffered composition comprising an organic acid and saltsthereof and a phosphorous-containing acid and salts thereof with waterto form a substantially fully solubilized use-dilution fertilizer havinga foliage-acceptable pH for phosphorus uptake, and applying saiduse-dilution fertilizer to the foliage of said plant.
 15. The method ofclaim 14 wherein said phosphorous-containing acid is selected from thegroup consisting of phosphorous acid, hypophosphorous acid,polyphosphorous acid, and polyhypophosphorous acid.
 16. The method ofclaim 14 wherein said organic acid is selected from the group consistingof dicarboxylic acids and tricarboxylic acids.
 17. The method of claim16 wherein said organic acid is citrate.
 18. The method of claim 14wherein said water has a pH of about 6.5 to about 8.5.
 19. The method ofclaim 14 wherein said use-dilution fertilizer comprises a ratio of saidconcentrated phosphorus fertilizer to said water of about 1:40 to about1:600.
 20. The method of claim 14 wherein said use-dilution fertilizerhas a pH of about 5.0 to about 7.0.
 21. The method of claim 14 whereinsaid use-dilution fertilizer has a pH of about 5.5 to about 6.5.
 22. Themethod of claim 14 wherein said plant is a citrus or avocado plant. 23.A method of providing phosphorus to a plant comprising distributing aliquid concentrated phosphorus fertilizer comprising a bufferedcomposition comprising an organic acid and salts thereof and aphosphorous-containing acid and salts thereof through an irrigationsystem and delivering said fertilizer to soil near said plant, saidfertilizer having a pH less than about 2.5.
 24. The method of claim 23wherein said fertilizer has a pH of less than about 1.5.